“The good news is that most corals appear to have this internal ability to buffer rising acidity of seawater and still form good, solid skeletons,” said ARC researcher Malcolm McCulloch. “Marine organisms that form calcium carbonate skeletons generally produce it in one of two forms, known as aragonite and calcite.

“Our research broadly suggests that those with skeletons made of aragonite have the coping mechanism – while those that follow the calcite pathway generally do less well under more acidic conditions.”

“But the picture for coral reefs as a whole isn’t quite so straightforward, as the ‘glue’ that holds coral reefs together – coralline algae – appear to be vulnerable to rising acidity,” McCulloch explained.

In a press release, the scientists said their discovery raises hopes that coral reefs might escape climatic devastation, as previously feared. The study was published in the journal Nature Climate Change.

Along with trapping heat in the atmosphere, rising levels of carbon dioxide are changing the chemical balance of oceans, turning them more acidic at rates exceeding previous climatic shifts. Many shell-forming species are thought to be very sensitive to those changes and some research suggests shellfish like mussels are already being affected.

Also of concern is that a large class of plankton, floating in the open oceans and forming a vital component of marine food webs, appears equally vulnerable to acidification. If so, this could be serious not only for marine life that feeds on them – but also for humans, as it could impair the oceans’ ability to soak up increased volumes of CO2 from the atmosphere. This would cause global warming to accelerate.

Ironically, an added plus is that warming oceans may increase the rates of coral growth, especially in corals now living in cooler waters, he says.

However, the big unknown remaining is whether corals can adapt to global warming, which is now occurring at an unprecedented rate – at about two orders of magnitude faster than occurred with the ending of the last Ice Age.

“This is crucial since, if corals are bleached by the sudden arrival of hot ocean water and lose the symbiotic algae which are their main source of energy, they will still die,” he cautions.

“It’s a more complicated picture, but broadly it means that there are going to be winners and losers in the oceans as its chemistry is modified by human activities – this could have the effect of altering major ocean ecosystems on which both we and a large part of marine life depend.”

The researchers concluded:

“Although our results indicate that up-regulation of pH at the site of calcification provides corals with enhanced resilience to the effects of ocean acidification, the overall health of coral reef systems is still largely dependent on the compounding effects of increasing thermal stress from global warming and local environmental impacts, such as terrestrial runoff, pollution and overfishing.”